Liquid crystal display and fabricating method thereof

ABSTRACT

A liquid crystal display device and a fabricating method thereof that are capable of preventing breakage of a pixel electrode. In the device, the protective layer pattern is provided at the overlapping area between the storage electrode and the pixel electrode to separate the storage electrode and the pixel electrode. Accordingly, the protective layer pattern is formed at the storage capacitor area to improve step coverage of a transparent conductive material.

This application claims the benefit of Korean Patent Application No.2000-85363 filed on Dec. 29, 2000, which is hereby incorporated byreference as if filly set forth herein.

BACKGROUND OF THF INVENTION

1. Field of the Invention

This invention relates to a liquid crystal display, and moreparticularly to a liquid crystal display and a fabricating methodthereof that are capable of preventing a breakage of a pixel electrode.

2. Discussion of the Related Art

Generally, a liquid crystal display (LCD) of active matrix drivingsystem uses thin film transistors (TFT's) as switching devices todisplay a natural moving picture. Since such an LCD can be made into asmaller device in size than a CRT, it has been widely used as a monitorfor a personal computer or a notebook computer, as well as in officeautomation equipment such as a copy machines, etc. and a portableequipment such as a cellular phone and a pager, etc.

Referring to FIG. 1 and FIG. 2, a lower substrate 1 of an LCD includes athin film transistor (TFT) T arranged at crossing area of a data line 4and a gate line 2, a pixel electrode 22 connected to a drain electrode10 of the TFT, and a storage capacitor S positioned at an overlappingportion between the pixel electrode 22 and the previous gate line 2.FIG. 2 is a cross-sectional view taken along I-I′ of FIG. 1.

The TFT T includes a gate electrode 6 connected to the gate line 2, asource electrode 8 connected to the data line 4, and a drain electrode10 connected, via a first contact hole 20 a, to the pixel electrode 22.Further, the TFT T includes semiconductor layers 14 and 16 for defininga channel between the source electrode 8 and the drain electrode 10 by agate voltage applied to the gate electrode 6. Such a TFT T responds to agate signal from the gate line 2 to selectively apply a data signal fromthe data line 4 to the pixel electrode 22.

The pixel electrode 22 is positioned at a cell area defined by the dataline 4 and the gate line 2 and is made from a transparent conductivematerial having a high light transmissivity. The pixel electrode 22generates a potential difference from a common transparent electrode(not shown) provided at an upper substrate (not shown) from a datasignal applied via the first contact hole 20 a. By this potentialdifference, a liquid crystal positioned between the lower substrate 1and the upper substrate (not shown) is rotated due to its dielectricanisotropy. Thus, the liquid crystal allows light applied from a lightsource to be transmitted into the upper substrate via the pixelelectrode 22.

The storage capacitor S charges a voltage as a gate high voltage isapplied to the previous gate line 2 and discharges the charged voltageas a data signal is applied to the pixel electrode to prevent a voltagevariation in the pixel electrode 22. The storage capacitor S consists ofa previous gate line 2 and a storage electrode 30 overlapping with thegate line 2 with a gate insulating film 12 therebetween. The storagecapacitor S is electrically connected to the pixel electrode 22 via asecond contact hole 20 b defined at a protective film 18.

Such a lower substrate 1 of the LCD requires at least five masks forpatterning each layer.

The gate electrode 6 is patterned with a first mask while thesemiconductor layers 14 and 16 are patterned with a second mask. Thestorage electrode 30 and the source and drain electrodes 8 and 10 arepatterned with a third mask while the first contact hole 20 a, thesecond contact hole 20 b and the protective layer 18 are patterned witha fourth mask. The pixel electrode 22 is patterned with a fifth mask.

FIG. 3A to FIG. 3E are sectional views for explaining a method offabricating the LCD device shown in FIG. 2 step by step.

Referring first to FIG. 3A, the gate electrode 6 and the gate line 2 areprovided on the substrate 1. The gate electrode 6 and the gate line 2are formed by depositing aluminum (Al) or copper (Cu), etc. using adeposition technique such as a sputtering, etc. and then patterning itwith the first mask.

Referring to FIG. 3B, an active layer 14 and an ohmic contact laser 16are provided on a gate insulating film 12.

The active layer 14 and the ohmic contact layer 16 are formed bydisposing the semiconductor layers 14 and 16 after forming the gateinsulating film 12 on the substrate 1 in such a manner to cover the gateelectrode 6 and then patterning them with the second mask.

The gate insulating film 12 is, formed by depositing an insulatingmaterial such as silicon nitride (SiN_(x)) or silicon oxide (SiO_(x)) bythe plasma enhanced chemical vapor deposition (PECVD) technique. Theactive layer 14 is formed from amorphous silicon that is not doped withan impurity. On the other hand the ohmic contact layer 16 is formed fromamorphous silicon doped with an n-type or p-type impurity at a highconcentration.

Referring to FIG. 3C, the storage electrode 30 and the source and drainelectrodes 8 and 10 are provided on the gate insulating film 12. Thestorage electrode 30 and the source and drain electrodes 8 and 10 areformed by entirely depositing a metal layer using the chemical vapordeposition (CVD) technique or the sputtering technique and thenpatterning it with the third mask. After the source and drain electrodes8 and 10 are patterned, the ohmic contact layer 16 at an areacorresponding to the gate electrode 6 also is patterned to expose theactive layer 14. The area of the active layer 14 corresponding to thegate electrode 6 between the source and drain electrodes 8 and 10 makesa channel. The storage electrode 30 and the source and drain electrodes8 and 10 are made from chrome (Cr) or molybdenum (Mo).

Referring to FIG. 3D, the protective layer 18 and the first and secondcontact holes 20 a, 20 b are provided on the gate insulating layer 12.The protective layer 18 and the first and second contact holes 20 a, 20b are formed by depositing an insulating material on the gate insulatinglayer 12 in such a manner to cover the storage electrode 30 and thesource and drain electrodes 8 and 10 and then patterning it with thefourth mask. The protective layer 18 is made from an inorganicinsulating material such as silicon nitride (SiN_(x)) or silicon oxide(SiO_(x)), an acrylic organic compound, or an organic insulatingmaterial having a small dielectric constant such as Teflon, BCB(benzocyclobutene), Cytop or PFCB (perfluorocyclobutane).

Referring to FIG. 3E, the pixel electrode 22 is provided on theprotective layer 18. The pixel electrode 22 is formed by depositing atransparent conductive material on the protective layer 18 and thenpatterning it with the fifth mask. The pixel electrode 22 iselectrically connected to the drain electrode 10 via the first contacthole 20 a and is electrically connected to the storage electrode 30 viathe second contact hole 20 b. The pixel electrode 22 is made from atransparent conductive material such as indium-tin-oxide (ITO),indium-zinc-oxide (IZO) or indium-tin-zinc-oxide (ITZO).

Although such a lower substrate of the liquid crystal display devicerequires a five-step mask process, it additionally requires at least twomasks for the purpose of preventing a hillock that may occur at analuminum surface when the gate electrode is made from aluminum.Accordingly, a construction of the lower substrate of the liquid crystaldisplays device requires at least a five- to seven-step mask process.

As the number of masks increases, the number of processes and processingtime not only increase when each layer is patterned, but also theproductivity and the yield are reduced. For this reason, there has beenactively conducted a study for reducing the number of masks.

FIG. 4 and FIG. 5 are a plan view and a sectional view, respectively,showing a lower substrate of the LCD employing a half-tone mask in afour-mask process.

Referring to FIG. 4 and FIG. 5 the lower substrate 1 of the LCD includesa thin film transistor (TFT) T arranged at a crossing area of a dataline 4 and a gate line 2, a pixel electrode 22 connected to a drainelectrode 10 of the TFT T, and a storage capacitor S positioned at anoverlapping portion between the pixel electrode 22 and the previous gateline 2.

The TFT T includes a gate electrode 6 connected to the gate line 2, asource electrode 8 connected to the data line 4, and a drain electrode10 connected to the pixel electrode 22 via a contact hole 20. Further,the TFT T includes semiconductor layers 14 and 16 for defining a channelbetween the source electrode 8 and the drain electrode 10 by a gatevoltage applied to the gate electrode 6. Such a TFT T responds to a gatesignal from the gate line 2 to selectively apply a data signal from thedata line 4 to the pixel electrode 22.

The pixel electrode 22 is positioned at a cell area defined by the dataline 4 and the gate line 2 and is made from 2 transparent conductivematerial having a high light transmissivity. The pixel electrode 22generates a potential difference from a common transparent electrode(not shown) provided at an upper substrate (not shown) from a datasignal applied via the contact hole 20. By this potential difference, aliquid crystal positioned between the lower substrate 1 and the uppersubstrate (not shown) is rotated due to its dielectric anisotropy. Thus,the liquid crystal allows a light applied from a light source to betransmitted into the upper substrate via the pixel electrode 22.

The storage capacitor S charges a voltage as a gate high voltage isapplied to the previous gate line 2, and discharges the charged voltageas a data signal is applied to the pixel electrode to prevent a voltagevariation in the pixel electrode 22. The storage capacitor S consists ofa previous gate line 2 and a storage electrode 30 overlapping with thegate line 2 with a gate insulating film 12 therebetween. The storagecapacitor S is directly connected to the pixel electrode 22.

Such a lower substrate 1 of the LCD requires at least four masks forpatterning each layer. The gate electrode 6 is patterned with a firstmask, while an ohmic contact layer 16, the storage electrode 30 and thesource and drain electrodes 8 and 10 are patterned with a second mask.The active layer 14, the contact hole 20 and the protective layer 18 arepatterned with a third mask, while the pixel electrode 22 is patternedwith a fourth mask.

Referring first to FIG. 6A, the gate line 2 and the gate electrode 6 areprovided on the substrate 1. The gate line 2 and the gate electrode 6are formed by depositing aluminum (Al) or copper (Cu) using a depositiontechnique such as a sputtering, etc. and then patterning it with thefirst mask.

Referring to FIG. 6B, the gate insulating film 12, the ohmic contactlayer 16, the storage electrode 30 and the source and drain electrodes 8and 10 are provided on the substrate 1. The gate insulating film 12 isformed by entirely depositing on the substrate 1 in such a manner tocover the gate electrode 6 and the gate line 2.

The ohmic contact layer 16, the storage electrode 30 and the source anddrain electrodes 8 and 10 are formed by depositing a first semiconductorlayer 14 a, a second semiconductor layer and a metal layer on the gateinsulating film 12 and then patterning the second semiconductor layerand the metal layer using the second mask. After the storage electrode30 and the source and drain electrodes 8 and 10 are patterned, the ohmiccontact layer 16 at an area corresponding to the gate electrode 6 alsois patterned to expose the first semiconductor layer 14 a. The areacorresponding to the gate electrode 6 between the source and drainelectrodes 8 and 10 at the first semiconductor layer 14 a makes achannel.

The gate insulating film 12 is formed by depositing an insulatingmaterial such as silicon nitride (SiN_(x)) or silicon oxide (SiO_(x)) bythe plasma enhanced chemical vapor deposition (PECVD). The firstsemiconductor layer 14 a, which is formed to be an active layer later,is formed from amorphous silicon that is not doped with on impurity. Onthe other hand, the ohmic contact layer 16 is formed from amorphoussilicon doped with an n-type or p-type impurity at a high concentration.The storage electrode 30 and the source and drain electrodes 8 and 10are formed from chrome (Cr) or molybdenum (Mo).

Referring to FIG. 6C, an insulating material 18 a ard a photoresist 24are provided on the first semiconductor layer 14 a. A half-tone mask 26that is the third mask having a transmissive part 26 a, asemi-transmissive part 26 b and a shielding part 26 c is positioned overthe photoresist 24. The shielding part 26 c is defined at an area laterto be provided with the protective film 18 of the TFT; the transmissivepart 26 a is defined at an area later to be provided with the contacthole 20 of the TFT; and the semi-transmissive part 26 b is defined atthe remaining area.

The half-tone mask 26 selectively irradiates ultraviolet light to thephotoresist 24 to expose it to the light.

The insulating material 18 a is made from an inorganic insulatingmaterial such as silicon nitride (SiN_(x)) or silicon oxide (SiO_(x)),an acrylic organic compound, or an organic insulating material having asmall dielectric constant such as Teflon, BCB (benzocyclobutene), Cytopor PFCB (perfluorocyclobutane).

Referring to FIG. 6D, a photoresist pattern 28 is formed on theinsulating material 18 a. The photoresist pattern 28 is formed bydeveloping the photoresist 24 with a developer such as alkali aqueoussolution. The photoresist pattern 28 having a thickness corresponding toapproximately 10 to 50% of the initial coating thickness is formed at anarea corresponding to the semi-transmissive part 26 b of the half-tonemask 26. The photoresist pattern 28 having the initial coating thicknessis formed at an area corresponding to the shielding part 26 c. Thephotoresist pattern 28 is removed at an area corresponding to thetransmissive part 26 a to thereby expose the insulating material 18 a.

Referring to FIG. 6E, the active layer 14, the protective layer 18 andthe contact hole 20 are provided on the gate insulating layer 12. Theactive layer 14, the protective layer 18 and the contact hole 20 areformed by exposing the lower substrate 1 provided with the photoresistpattern 28 to an etchant to simultaneously etch the insulating material18 a and the first semiconductor layer 14 a. After the active layer 14,the protective layer 18 and the contact hole 20 are formed, thephotoresist pattern 28 is removed.

Referring to FIG. 6F, the pixel electrode 22 is provided on theprotective layer 18. The pixel electrode 22 is formed by depositing atransparent conductive material such as indium-tin-oxide (ITO),indium-zinc-oxide (IZO) or indium-tin-zinc-oxide (ITZO) on theprotective layer 18 and then patterning it using the fourth mask. Thepixel electrode 22 is electrically connected to the drain electrode 10via the contact hole 20, and is directly connected to the storageelectrode 30 with no contact hole.

On the storage capacitor area S of the LCD, as shown in FIG. 6D, thephotoresist pattern 28 is remained about 10 to 50 percents. After thecontact hole 20 is formed, the area of the photoresist pattern 28corresponding to the semi-transmissive part 26 b of the half-tone mask26 is removed by an ashing process. After all, the photoresist pattern28 for forming the protective layer 18 and the active layer 14 are notprovided on the storage capacitor area S. In other words, if the storagecapacitor area S at the lower substrate 1 of the LCD is exposed to anetchant, then the protective layer 18 is entirely removed by the dryetching while the active layer 14 is left only at the lower portion ofthe storage electrode 30 formed by the wet etching. Since an eddyphenomenon is generated at the side surface of the active layer 14 whenthe active layer 14 is etched, the active layer 14 under the edge of thestorage electrode 30 is more undercut than the storage electrode 30 toform a step coverage or an overhang, as shown in FIG. 7. If atransparent conductive material is deposited onto the gate insulatingfilm 12 on which the active layer 14 is formed in the step coverage, thetransparent conductive material is non-uniformly deposited at the stepcoverage area. For this reason, the conventional LCD has a problem inthat, when the lower substrate 1 of the LCD is dipped into an etchant toetch the transparent conductive material, the pixel electrode 22 issusceptible to breakage at the step coverage area.

SUMMARY OF THF INVENTION

Accordingly, the present invention is directed to Liquid Crystal DisplayFabrication, Method Thereof that substantially obviates one or more ofthe problems due to limitations and disadvantages of the related art.

Accordingly, it is an advantage of the present invention to provide aliquid crystal display and a fabricating method thereof that is capableof preventing breakage of a pixel electrode.

In order to achieve these and other advantages of the invention, aliquid crystal display device according to one aspect of the presentinvention includes a data line supplied with a data signal, a gate linesupplied with a scanning signal, a pixel electrode for driving a liquidcrystal cell, and a thin film transistor for responding to the scanningsignal to switch the data signal into the pixel electrode, a storageelectrode overlapping with the gate line and constituting a storagecapacitor, and, a protective layer pattern being formed separatedbetween the storage electrode and the pixel electrode at an overlappingarea between the storage electrode and the pixel electrode.

In the liquid crystal display device, the storage capacitor areaincludes a gate insulating film formed on a substrate in such a mannerto cover the gate line; and a semiconductor layer between the gateinsulating film and the storage electrode.

In the liquid crystal display device, the protective layer is separatelyformed at each edge of both lower sides of the storage capacitor area.

The liquid crystal display device, further includes a gate electrodeformed to connect with the gate line on the substrate; a gate insulatingfilm formed on the substrate; a semiconductor layer formed on the gateinsulating film; a source electrode and a drain electrode formed on thegate insulating film; and a protective layer formed between the gateinsulating film and the pixel electrode.

In the liquid crystal display device, the semiconductor layer is formedwith an active layer and an ohmic contact layer, and the active layer isformed in the same pattern as the protective layer and the ohmic contactlayer is formed in the same pattern as the source electrode and thedrain electrode.

A liquid crystal display device according to another aspect of thepresent invention includes a data line supplied with a data signal, agate line supplied with a scanning signal, a pixel electrode for drivinga liquid crystal cell, and a thin film transistor for responding to thescanning signal to switch the data signal into the pixel electrode, astorage electrode overlapping with the gate line and constituting astorage capacitor, and a pixel electrode extended into each side edgeand the upper edge of the storage electrode.

In the liquid crystal display devices the storage capacitor areaincludes the gate line provided on a substrate; a gate insulating filmformed on the substrate in order to cover the ate line; and asemiconductor layer formed on the gate insulating film in the samepattern as the storage electrode simultaneously.

The liquid crystal display device, further includes a gate electrodeformed to connect with the gate line on the substrate; a gate insulatingfilm formed on the substrate; a semiconductor layer formed on the gateinsulating film; a source electrode and a drain electrode formed on thegate insulating film; a protective layer formed on the gate insulatingfilm; and the pixel electrode formed on the protective layer.

In the liquid crystal display device, the semiconductor layer is formedwith an active layer and an ohmic contact layer, and the active layer isformed in the same pattern as the protective layer and the ohmic contactlayer is formed in the same pattern as the source electrode and thedrain electrode.

A method of fabricating a liquid crystal display device according tostill another aspect of the present invention includes forming a gateline on a substrate, forming a gate insulating film on the substrate insuch a manner to cover the gate line; forming an ohmic contact layer anda storage electrode by entirely depositing a first semiconductor layer,a second semiconductor layer and a metal layer onto the gate insulatingfilm and then simultaneously patterning the second semiconductor layerand the metal layer into the same pattern; forming an active layer and aprotective layer by depositing an insulating material onto the firstsemiconductor layer and then patterning the first semiconductor layerand the insulating material; and forming a pixel electrode by depositinga transparent conductive material onto the gate insulating film and thenpatterning it.

In the method, the protective layer is separately formed at each loweredge of the storage capacitor area.

The method further includes forming a gate electrode on the substrate;forming a gate insulating film on the substrate on which the gateelectrode is formed; forming an ohmic contact layer and source and drainelectrodes on the gate insulating film in the same patternsimultaneously; forming an active layer and a protective layer on thegate insulating film in the same pattern simultaneously; and forming apixel electrode on the protective layer.

A method of fabricating a liquid crystal display device according tostill another aspect of the present invention includes forming a gateline on a substrate; forming a gate insulating film on the substrate insuch a manner to cover the gate line: forming an ohmic contact layer anda storage electrode by entirely depositing a first semiconductor layer,a second semiconductor layer and a metal layer onto the gate insulatingfilm and then simultaneously patterning the second semiconductor layerand the metal layer into the same pattern; forming an active layer bydepositing an insulating material onto the first semiconductor layer andthen simultaneously patterning the first semiconductor layer and theinsulating material; and forming a pixel electrode by depositing atransparent conductive material onto the gate insulating film at an areaextended into each side edge and the upper edge of the storage electrodeand then patterning it.

The method further includes forming a gate electrode on the substrate;forming a gate insulating film on the substrate in such a manner tocover the gate electrode; forming an ohmic contact layer and source anddrain electrodes on the gate insulating film in the same patternsimultaneously; forming an active layer and a protective layer on thegate insulating film in the same pattern simultaneously; and forming apixel electrode on the gate insulating film.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

These and other advantages of the invention will be apparent from thefollowing detailed description of the embodiments of the presentinvention with reference to the accompanying drawings, in which, in thedrawings:

FIG. 1 is a plan view showing a structure of a conventional liquidcrystal display device formed with five masks;

FIG. 2 is a section view of the liquid crystal display device takenalong the I-I′ line in FIG. 1;

FIG. 3A to FIG. 3E are section views representing step by step a methodof fabricating the liquid crystal display device shown in FIG. 2;

FIG. 4 is a plan view showing a structure of a conventional thin filmtransistor formed with a half-tone mask;

FIG. 5 is a section view of the liquid crystal display device takenalong the II-II′ line in FIG. 4;

FIG. 6A to FIG. 6E are section views representing step by step a methodof fabricating the liquid crystal display device shown in FIG. 5;

FIG. 7 is a section view of the undercut active layer of the liquidcrystal display device shown in FIG. 5;

FIG. 8 is a plan view showing a structure of a liquid crystal displaydevice according to a first embodiment of the present invention;

FIG. 9 is a section view of the liquid crystal display device takenalong the III-III′ line in FIG. 8;

FIG. 10A to FIG. 10F are section views representing step by step amethod of fabricating the liquid crystal display device shown in FIG. 9;

FIG. 11 is a plan view showing a structure of a liquid crystal displaydevice according to a second embodiment of the present invention; and

FIG. 12 is a section view of the liquid crystal display device takenalong the IV-IV′ line in FIG. 11.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to an embodiment of the presentinvention, example of which is illustrated in the accompanying drawings.

Referring to FIG. 8 and FIG. 9, there is shown a lower substrate 31 of aliquid crystal display (LCD) according to a first embodiment of thepresent invention includes a TFT T arranged at a crossing of a data line34 and a gate line 32, a pixel electrode 52 connected to a drainelectrode 40 of the TFT T, and a storage capacitor S positioned at anoverlapping portion between the pixel electrode 52 and the previous gateline 32.

The TFT T includes a gate electrode 36 connected to the gate line 32, asource electrode 38 connected to the data line 34, and a drain electrode40 connected to the pixel electrode 52 via a contact hole 50. Further,the TFT T includes semiconductor layers 44 and 46 for defining a channelbetween the source electrode 38 and the drain electrode 40 by a gatevoltage applied to the gate electrode 36. Such a TFT responds to a gatesignal from the gate line 32 to selectively apply a data signal from thedata line 34 to the pixel electrode 52.

The pixel electrode 52 is positioned at a cell area defined by the dataline 34 and the gate line 32. The pixel electrode 52 is made from atransparent conductive material having a high light transmissivity. Thepixel electrode 52 generates a potential difference between a commontransparent electrode (not shown) provided at an upper substrate (notshown) and a data signal applied via the contact hole 50. By thispotential difference, a liquid crystal positioned between the lowersubstrate and the upper substrate is rotated due to its dielectricanisotropy. Thus, the liquid crystal allows a light applied, via thepixel electrode 52, from a light source to be transmitted into the uppersubstrate.

The storage capacitor S charges a voltage during application of a gatehigh voltage to the previous gate line 32 and discharges the chargedvoltage during application of a data signal to the pixel electrode 52,to thereby prevent a voltage variation in the pixel electrode 52. Thestorage capacitor S consists of a previous gate line 32 and a storageelectrode 60 overlapping with the gate line 32 with a gate insulatingfilm 42 therebetween. The storage electrode is electrically connected tothe pixel electrode 52. A protective layer pattern 62 is provided at theedge of said overlapping area between the storage electrode 60 and thepixel electrode 52.

The lower substrate 31 of the LCD requires four masks for patterningeach layer. The gate electrode 36 is patterned with a first mask, whitean ohmic contact layer 46, the storage electrode 60 and the source anddrain electrodes 38 and 40 are patterned with a second mask. The activelayer 44, the contact hole 50, the protective layer pattern 62 and theprotective layer 48 are patterned with a third mask, while the pixelelectrode 52 is patterned with a fourth mask.

FIG. 10A to FIG. 10F are section views and plan views for explaining amethod of fabricating the LCD device shown in FIG. 8 step by step alongline III-III′.

Referring first to FIG. 10A, the gate line 32 and the gate electrode 36are provided on the substrate 31. The gate line 32 and the gateelectrode 36 are formed by depositing aluminum (Al) or copper (Cu) by adeposition technique such as a sputtering, etc. and then patterning itwith the first mask.

Referring to FIG. 10B, the gate insulating film 42, the ohmic contactlayer 46, the storage electrode 60, the source electrode 38 and thedrain electrode 40 are provided on the substrate 31. The gate insulatingfilm 42 is formed by entirely depositing an insulating material on thesubstrate 31 in such a manner to cover the gate electrode 36 and thegate line 32.

The storage electrode 60 and the source and drain electrodes 38 and 40are formed by entirely depositing a first semiconductor layer 44 a, asecond semiconductor layer and a metal layer on the gate insulating film42 and then patterning the second semiconductor layer and the metallayer using the second mask. After the storage electrode 60 and thesource and drain electrodes 38 and 40 are patterned, the ohmic contactlayer 46 at an area corresponding to the gate electrode 36 and the gateline 32 is also patterned to expose the first semiconductor layer 44 a.A portion of the first semiconductor layer 44 a corresponding to thegate electrode 36 between the source and drain electrodes 38 and 40 atthe first semiconductor layer 44 a makes a channel.

The gate insulating film 42 is formed by depositing an insulatingmaterial such as silicon nitride (SiN_(x)) or silicon oxide (SiO_(x)) bythe plasma enhanced chemical vapor deposition (PECVD) or other method.The first semiconductor layer 44 a is formed from amorphous silicon thatis not doped with an impurity. On the other hand, the ohmic contactlayer 46 is formed from amorphous silicon doped with an n-type or p-typeimpurity at a high concentration. The storage electrode 60 and thesource and drain electrodes 38 and 40 are formed from chrome (Cr) ormolybdenum (Mo) or the like.

Referring to FIG. 1C, an insulating material 48 a and a photoresist 54are provided on the gate insulating film 42.

The third mask is a half-tone mask 56 having a transmissive part 56 a, asemi-transmissive part 56 b and a shielding part 56 c positioned overthe photoresist 54. The shielding part 56 c of the half-tone mask 56 isdefined at an area later to be provided with the protective film of theTFT and a protective layer pattern at the storage capacitor area. Thetransmissive part 56 a is defined at an area later to be provided withthe contact hole of the TFT. The semi-transmissive part 56 b is definedat the remaining area. The half-tone mask 56 selectively irradiatesultraviolet light to the photoresist 54 to expose it to the light.

The insulating material 48 a is made from an inorganic insulatingmaterial such as silicon nitride (SiN_(x)) or silicon oxide (SiO_(x)),an acrylic organic compound, or an organic insulating material having asmall dielectric constant such as Teflon, BCB (benzocyclobutene), Cytopor PFCB (perfluorocyclobutane).

Referring to FIG. 10D, a photoresist pattern 58 is formed on theinsulating material 48 a. The photoresist pattern 58 is formed bydeveloping the photoresist 54 with a developer such as alkali aqueoussolution.

The photoresist pattern 58 having a thickness corresponding toapproximately 10 to 50% of the initial coating thickness is formed at anarea corresponding to the semi-transmissive part 56 b of the half-tonemask 56. The photoresist pattern 58 having the initial coating,thickness is formed at an area corresponding to the shielding part 56 c;and the photoresist pattern 58 is removed at an area corresponding tothe transmission part 56 a to thereby expose the insulating material 48a.

Referring to FIG. 10E, the active layer 44, the protective layer pattern62 at the storage capacitor area S, the protective layer 48 of the TFT Tand the contact hole 50 are provided on the gate insulating layer 42.The active layer 44, the protective layer pattern 62, the protectivelayer 48 and the contact hole 50 are formed by exposing the substrate 31provided with the photoresist pattern 58 to an etchant and thensimultaneously etching the insulating material 48 a and the firstsemiconductor layer 44 a. After the active layer 44, the protectivelayer pattern 62, the protective layer 48 and the contact hole 50 areformed, the photoresist pattern 58 is removed.

Referring to FIG. 10F, the pixel electrode 52 is provided on theprotective layer 48. The pixel electrode 52 is formed by depositing atransparent conductive material such as indium-tin-oxide (ITO),indium-zinc-oxide (IZO) or indium-tin-zinc-oxide (ITZO) on theprotective layer 48 and then patterning it using the fourth mask. Thepixel electrode 52 directly contacts the storage electrode 60 withoutany contact hole and electrically connected to the drain electrode 40via the contact hole 50.

As described above, the protective layer pattern 62 is provided on theedges of the storage electrode 60. Because the protective layer pattern62 and the active layer 44 has a similar etching selectivity, the endportions of the protective layer pattern 62 and active layer 44 has asmooth slope. Accordingly, a step coverage of a transparent conductivematerial is improved on the protective layer pattern 62 and active layer44, so that it becomes possible to prevent breakage of the pixelelectrode 52.

Referring to FIG. 11 and FIG. 12, a lower substrate of a liquid crystaldisplay, device according, to a second embodiment of the presentinvention has the same elements as the liquid crystal display deviceshown in FIG. 8, except that a pixel electrode 52 takes a substantiallyrounded shape of surrounding a storage electrode 60. FIG. 12 is across-sectional view of FIG. 11 taken along line IV-IV′.

The pixel electrode 52 is formed in the pixel area and extends into eachedge of all sides of the storage electrode 60 except the area of thestorage electrode 60, as shown in FIG. 11. Consequently, the lowerportion of the pixel electrode 52 is not provided with the active layer(not shown) and the storage electrode 60. Thus, the pixel electrode 52is uniformly deposited onto the gate insulating film 42. A storagecapacitor is formed with the storage electrode 60 and the gate line 32having the gate insulating film 42 in between them.

Hereinafter, a method of fabricating the lower substrate of the LCDdevice having the structure as mentioned above will be brieflydescribed.

A gate metal layer is deposited onto the substrate 31 and then patternedto form the gate line 32 and the gate electrode 36, and thereafter thegate insulating film 42 is entirely coated thereon. The firstsemiconductor layer, the second semiconductor layer and the metal layerare entirely coated on the gate insulating film 42, and then the secondsemiconductor layer and the metal layer are patterned, to thereby formthe ohmic contact layer (not shown), the storage electrode 60 and thesource and drain electrodes 38 and 40. Subsequently, the insulatingmaterial is entirely deposited onto the first semiconductor layer andthen the insulating material and the first semiconductor layer arepatterned, to thereby form the contact hole 50, the active layer (notshown) and the protective film (not shown). A transparent electrodematerial is deposited onto the protective film (not shown) and thenpatterned, to thereby form the pixel electrode 52.

As described above, according to the first embodiment of the presentinvention, the protective layer pattern 62 is provided or, the edges ofthe storage electrode 60. Because the protective layer pattern 62 andthe active layer 44 has a similar etching selectivity, the end portionsof the protective layer pattern 62 and active layer 44 has a smoothslope. Accordingly, a step coverage of a transparent conductive materialis improved on the protective layer pattern 62 and active layer 44, sothat it becomes possible to prevent breakage of the pixel electrode 52.

Furthermore, according to the second embodiment of the presentinvention, the pixel electrode is formed to cover entirely the surfaceand all side edges of the storage electrode, so that it also becomespossible to prevent breakage of the pixel electrode.

Although the present invention has been explained by the embodimentsshown in the drawings described above, it should be understood to theordinary skilled person in the art that the invention is not limited tothe embodiments, but rather that various chances or modificationsthereof are possible without departing from the spirit of the invention.Accordingly, the scope of the invention shall be determined only by theappended claims and their equivalents.

1-9. (canceled)
 10. A method of fabricating a liquid crystal displaydevice, comprising: forming a gate line on a substrate; forming a gateinsulating film on said substrate to cover the gate line; forming anohmic contact layer and a storage electrode by entirely depositing afirst semiconductor layer, a second semiconductor layer and a metallayer onto said gate insulating film and then simultaneously patterningthe second semiconductor layer and the metal layer into the samepattern; forming an active layer and a protective layer by depositing aninsulating material onto the first semiconductor layer and thenpatterning the first semiconductor layer and the insulating material,and forming a pixel electrode by depositing a transparent conductivematerial onto gate insulating film and then patterning the transparentconductive material.
 11. The method according to claim 10, wherein theprotective layer is separately formed at each lower edge of the storagecapacitor area.
 12. The method according to claim 10, furthercomprising: forming a gate electrode on the substrate; forming a gateinsulating film on the substrate; forming an ohmic contact layer andsource and drain electrodes on the gate insulating film in the samepattern simultaneously; forming an active layer and a protective layeron the gate insulating film in the same pattern simultaneously; andforming a pixel electrode on the protective layer.
 13. A method offabricating a liquid crystal display device, comprising: forming a gateline on a substrate; forming a gate insulating film on the substrate insuch a manner to cover the gate line; forming an ohmic contact layer anda storage electrode by entirely depositing a first semiconductor layer,a second semiconductor layer and a metal layer onto the gate insulatingfilm and then simultaneously-patterning the second semiconductor layerand the metal layer into the same pattern; forming an active layer bydepositing an insulating material onto the first semiconductor layer andthen simultaneously patterning the first semiconductor layer and theinsulating material; and forming a pixel electrode by depositing atransparent conductive material onto the gate insulating film at an areaextended into an upper edge and each side edge of the storage electrodeand then patterning the transparent conductive material.
 14. The methodaccording to claim 13, further comprising: forming a gate electrode onthe substrate; forming a gate insulating film on the substrate to coverthe gate electrode; forming an ohmic contact layer and source and drainelectrodes on the gate insulating film in the same patternsimultaneously; forming an active layer and a protective layer on thegate insulating film in the same pattern simultaneously; and forming apixel electrode on the gate insulating film. 15-19. (canceled)